The Flood Memory project examines observed records of storms to help us better understand how clustering of hydrological events may obscure or even exacerbate climate induced changes. The project investigates the most critical flood scenarios caused by sequences or clusters of extreme weather events striking vulnerable systems of flood defences, urban areas, communities and businesses.
The team analyse and simulate situations where a second flood may strike before coastal or river defences have been reinstated after damage, or householders and small businesses are in a vulnerable condition recovering from the first flood. By examining such events and identifying the worst case scenarios, we hope our findings will lead to enhanced flood resilience and better allocation of resources for protection and recovery.
Typically, the design and analysis of fluvial flood defence schemes is based on a single N year extreme flow event using a single survey of the river channel and floodplains. Adopting such an approach assumes that the capacity of the channel is identical for all subsequent N year events, thus failing to account for the morphodynamic memory of the system as a result of the antecedent flow regime. Recent academic studies, and flood events (e.g. Somerset Levels 2013/14), have shown that changes to the channel geometry, as a result of sedimentation, can significantly increase the flood risk. To provide a more robust estimate of future flood risk, the uncertainties associated with these changes should be accounted for in inundation modelling and flood defence scheme design. Thus, the aim of the work conducted here is to develop modelling methods incorporate these changes into future flood risk assessments.
Recent work conducted here has shown that, the sequencing in which flood events occur can have a significant influence on the subsequent changes in river channel geometry. As such, current work involves the simulation of sediment transport and morphological changes for multiple 50 year flow sequences on the River Caldew, UK. The sediment transport and changes in channel geometry have been predicted using the, commonly applied, 1D HEC-RAS model. Results from these changes were then used to define a potential ‘worst-case’ future channel configuration, used to assess the impacts of future flood events, using 1D and 2D hydrodynamic models. Results show that the effects of 50 years of morphological change can result in significant increases in future flood risk. Additionally, at higher frequency events, these changes can turn previous in-bank high flow events to out-of-bank flood events as shown in Fig. 1.
Fig. 1: Flood extents predicted from a 1D/2D hydrodynamic model using (a) the original channel configuration and (b) the worst-case potential configuration after 50 years of morphological change
An additional information document regarding this project can be accessed here: Factsheet WS3
For further information please visit http://wateracademy.org.uk/flood-memory.
Contacts: Heather Haynes firstname.lastname@example.org at Heriot-Watt University, Edinburgh